Mercury pool discharge device



15, 1963 R. B. CUSTER ETAL 3,073,983

MERCURY POOL DISCHARGE DEVICE Filed July 21, 1959 35' 7E 27 Tar-5 FPOLLA B. CUsTE F CLARE/v05 HELD "i taes Calif.

Filed July 21, 1959, Ser. No. 828,514 4 Claims. (Cl. 313--165) This invention relates to mercury pool discharge devices and more particularly to an improved tube for such devices.

An object of the present invention is to provide a double mercury pool type tube wherein the mercury vapor or plasma must travel only a very short distance with the result that the tube has a low plasma arc drop voltage and low power loss in the tube in relation to its electrical rating.

Ano her object is to provide an improved, liquid cooled mercury pool type anode electrode that is free from damage from heat, electrical overloads, arc-backs, mercury vapor ion bombardment and gas release and by the limitations of radiation cooling such as is the case with tubes using internal carbon anodes.

A further object is to provide an improved liquid cooled mercury pool type cathode electrode.

Another object is to provide an effective automatic mercury level control for a double mercury pool type tube.

Another object of the present invention is to provide a tube design which facilitates the design and construction of a ceramic insulator having metal-ceramic seals that are vacuum-tight, mechanically strong and easily manufactured.

A further object is to provide a tube which is constructed of high temperature melting point metal and ceramic materials, and which can be heat treated and degassed in order to obtain very high vacuum.

Another object is to provide a tube design wherein all the component parts can be made in molds or dies or can be machined to close dimensions for production line assembly.

A further object is to provide a tube design which simplifies the construction and attachment of liquid cooling jackets.

Another object is to provide an improved cooling jacket which can also be used for high capacity current terminals and for tube mounting means.

Other and further objects and advantages of the present invention will be apparent from the following description taken in connection with the accompanying drawing which illustrates, more or less diagrammatically, a vertical central section through the tube of the present invention.

In the tube of the present invention an anode mercury pool A is disposed in spaced relation above a cathode mercury pool C. The anode pool A is contained in an annular retainer which is formed by a lower generally cylindrical wall 12a of a generally hemi-spherical metal dome 12, an annular base plate 14 which is welded at 15 to the end wall 12a, a cylinder 15 which is welded to and projects downwardly from the inner circular edge of annular plate 14, an annular horizontal surface lea of a ring-shaped ceramic insulator 18, and an upwardly projecting wall 18b of the insulator ring. The annular plate 14 and the cylinder 16 may be made of stainless steel or Kovar, while the insulator ring 18 may be made of very high purity aluminum oxide powder or a material having similar insulating properties.

The cathode mercin'y pool is retained in a metal container 22. which has a circular base plate 22a of stainless steel or Kovar to the periphery of which is welded a cylinder 22%) of similar material. The cylinder 22b is ice molded and fused in the ceramic insulator 18 so that the inner cylindrical Wall 180 of the insulator ring forms the upper side wall of the cathode pool container.

The metal dome 12 has an upper central opening Sil and the annular portion of the dome around the opening is fused in a second ceramic insulator 52 which may be made of aluminum oxide powder or the like. A tungsten rod 54 is fused in the insulator 52 and extends downwardly through the insulator into the tube. Connected to the lower end of the rod 54 is an igniter or control electrode 56 which projects down into the mercury of the cathode pool so that an electric current may be passed through the mercury to cause a spark which will initiate the start of conduction or discharge of current from the cathode pool to the anode pool. For certain installations, a keep-alive anode 58 may be fused in the ceramic insulator 52. The inside surface of the metal dome 12 is lined with a coating 60 of an insulating, ceramic-enamel, high temperature type material which is fused on the inner surface of the dome in a high temperature furnace. The coating 66 prevent the metal of the dome from becoming an active part of the anode electrode and decomposing due to ion bombardment.

From the foregoing description, it will be noted that the envelope of the tube is formed by the closed dome 12, the annular base plate 14, the cylinder 16, the insulating ring 18, and the container 22.

It will be noted also that the cathode pool C is directly and coaxially under the opening in the center of the anode pool A. This orientation of the electrodes permits the current conducting plasma discharge to flow upward from the surface of the cathode pool to all parts of the surface of the anode pool. The distance of travel for the plasma is very short and, as a result, the tube has a very low arc drop power loss. The anode pool A is made much larger than the cathode pool because there is more heat developed at the anode than at the cathode.

A copper cooling jacket 79, which is brazed to the lower surface of the base plate 14, is provided with passages 72 through which water, oil, or a refrigerant may be circulated to maintain the temperature of the mercury in the anode pool within a proper operating range. This copper jacket is also used to provide terminal for connection of conventional current carrying conductors. Similarly, a second copper cooling jacket 75, which is brazed to the external side of the base plate 22a of container 22, is provided with passages 76 for a liquid coolant. It is to be particularly noted that the circular area of contact between the plate 22a and the jacket is large compared to the area of the upper surface of the cathode pool. With this arrangement, particularly eifective cooling of the cathode pool is obtained. The jacket 75' also functions as the cathode current terminal and as a means for bolting the tube to a buss bar for mounting purposes.

The external surface of the dome 12 is cooled by means of air forced thereover, or by means of a cooling jacket (not shown) similar to cooling jackets 70 and 75.

Means is provided for maintaining the surface of the anode pool at a desired level. During operation, mercury is condensed on the cooled, generally sphericalshaped inner surface of the dome 12 and, as drops are formed, they drop back into the anode pool. This automatic level control device comprises a small diameter metal tube 80 which is fused in and projects through the upstanding annular wall 18b of insulator 18 at a point somewhat below the desired surface level of the anode pool. The tube 80 is bent upward at a right angle, and its upper overflow lip or edge is at an elevation equal to the desired level of the surface of the mercury in the anode pool. When the surface of the mercury in the anode pool rises above the desired level, the excess mer- '2 u cury will pass over the upper edge of the overflow tube and a drop at a time will fall down into the cathode pool. With this arrangement the exact desired level is automatically maintained without the danger of a short circuit, such as would occur if mercury were allowed to flow to the cathode pool in a solid stream.

The exposed part of the overflow tube is shielded from the plasma rising from the cathode pool by means of a generally semi-cylindrical cover 82 which is closed at its upper end and has a lower open end projecting down into the cathode pool. The longitudinal edges of this ce ramic cover 82 are disposed in close sealing engagement with the inner wall of the insulator ring18 and therefore the plasma cannot use the overflow tube as a short cut to the anode. If for any reason excess mercury enters the cathode pool, it may be removed by turning the tube upside-down for a moment and then returning it to upright position. The mercury will automatically level off at each pool.

As mentioned above, the insulator ring 18 forms part of the envelope of the tube. Accordingly, it is necessary that vacuum tight seals be formed between the insulator ring and the adjacent parts of the envelope. In accordance with the present invention, the insulator is molded of aluminum oxide powder or like material with the two cylindrical members 16 and 22b embedded therein, under very high pressure in a steel mold. After the molding operation, the composite member is sintered in a high temperature furnace until it becomes a solid fused body which is resistant to heat and mechanical stress and strain. The cylinders 16 and 22b form, efiicient vacuum tight seals with the ceramic and, for this reason, the cylinders are electroplated with silver or copper and have holes cut in them in the area embedded in the insulator to enable the ceramic material to form a better bond at the interface, and also to make possible a stronger grip of the ceramic material on the metal. The metal is thin, the gage being such that the slight difference in the coefficients of expansion of the two materials cannot cause cracking or other damage. Further, the insulator ring is made very thick and is therefore much stronger than the metal cylinders.

All materials used in the construction of the tube can withstand high temperature and will not contaminate mercury under any condition. This enables the tube to be degassed and evacuated in a high temperature bake out oven with the result that an excellent vacuum is more readily obtained, after which mercury may be distilled into the tube and the evacuating tubulation 99,

which is fused into and through the top ceramic insulater 52, is sealed E.

In operation, the only exposed electrode material is mercury, which cannot be damaged by bombardment of mercury vapor ions, arc-backs, or heat. The aluminum oxide coating and insulator are also inert to the effects of heat and mercury arc bombardment, and so is tungsten. Therefore, the current conducting capacity is limited only by the mercury vapor pressure, which if too high can prevent the operation of the tube, but cannot damage it and, since the vapor pressure is kept under control by the efiicient cooling system, the current capacity is directly related to the rate of flow of the liquid coolant through the jackets that are mounted under the pools and to the cooling of the upper dome. In the present tube the cooling is very eifective because almost the complete outer area of the tube is cooled and, accordingly, heat is removed just as fast as it is developed.

The tube design of the present invention makes possible the control of extremely large currents by a tube having quite small physical dimensions. For example, in a tube 12 inches in diameter and 9 inches high, there will be an anode electrode in the form of a mercury pool with an area of 100 square inches and a mercury pool type cathode with an area of 8 square inches. Since both electrodes are forced liquid cooled, a continuous current rating of several thousand amperes is permitted. This is an improvement over present commercial tubes using a radiation cooled carbon anode by a factor of about 50, on the basis of cubic inch of tube size per watt of power controlled.

While we have described a particular embodiment of the invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from our invention in its broader aspects, and we aim, therefore, to cover in the appended claims all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to protect by Letters Patent is:

In a mercury pool rectifier tube, an envelope comprising a dome shaped member closed at its upper end and open at its lower end, an annular anode pool container having a first wall connected to the lower end of said dome shaped member and a second wall projecting both upwardly and downwardly from said first wall, a cup shaped cathode pool container disposed below said annular container and having an upstanding side wall, and an annular insulator in vacuum tight engagement with the downwardly projecting wall of said anode container and the upstanding side wall of said cup shaped container.

2. In a mercury pool discharge tube, a first container adapted to retain a mercury anode pool, an overflow pipe associated with said first container and having an over flow lip determining the height of the mercury in the anode pool, a second container adapted to hold a mercury cathode pool disposed directly below said overflow lip to receive mercury overflowing from said anode pool, and means defining an insulated conduit enclosing said overflow pipe and providing a passage for said overflowing mercury that is shielded from the path of movement of plasma leaving the cathode pool.

3. In a mercury pool discharge device, a closed hollow body, a pair of spaced pools of mercury disposed within said body and providing an anode pool spaced above a cathode pool with a passageway therebetween permitting vaporized mercury from said cathode pool to move toward said anode pool, an overflow conduit communicating with said anode pool and projecting into said vapor passageway, and means disposed in said passageway and enclosing said overflow conduit to isolate the interior of said conduit from vapor flowing through said passageway and to provide flow communication between said overflow conduit and said cathode pool.

4. In a mercury pool rectifier tube, a cathode electrode comprising an insulator having a central opening and an annular lower wall, a metal cup shaped member disposed below said insulator and having a base larger in crosssectional area than the area of said central opening and having an upstanding wall embedded in said insulator at a point spaced radially outwardly from said central opening, and a pool of mercury disposed in said cup shaped member and extending under said annular lower wall and upwardly into the central opening of said insulator.

References Cited in the file of this patent UNITED STATES PATENTS 1,715,874 Szilard June 4, 1929 1,740,030 Nagoaka et al Dec. 17, 1929 1,834,809 Swann Dec. 1, 1931 1,865,512 Gaudenzi July 5, 1932. 2,413,175 Dawley Dec. 24, 1946 2,516,736 Warmoltz July 25, 1950 2,919,367 Hernqvist Dec. 29, 1959 2,963,614 Riebs Dec. 6, 1960 

1. IN A MERCURY POOL RECTIFIER TUBE, AN ENVELOPE COMPRISING A DOME SHAPED MEMBER CLOSED AT ITS UPPER END AND OPEN AT ITS LOWER END, AN ANNULAR ANODE POOL CONTAINER HAVING A FIRST WALL CONNECTED TO THE LOWER END OF SAID DOME SHAPED MEMBER AND A SECOND WALL PROJECTING BOTH UPWARDLY AND DOWNWARDLY FROM SAID FIRST WALL, A CUP SHAPED CATHODE POOL CONTAINER DISPOSED BELOW SAID ANNULAR CONTAINER AND HAVING AN UPSTANDING SIDE WALL, AND AN ANNULAR INSULATOR IN VACUUM TIGHT ENGAGEMENT WITH THE DOWNWARDLY PROJECTING WALL OF SAID ANODE CONTAINER AND THE UPSTANDING SIDE WALL OF SAID CUP SHAPED CONTAINER. 